1. Field
This invention pertains to ultrasonic, non-destructive evaluation and testing, and more particularly, to systems and methods for the inspection of piping for the presence of defects, flaws and discontinuities, using Lamb-type wave transducers.
2. Description of Related Art
Non-destructive evaluation (NDE) methods, such as ultrasonic testing (UT), are known in the art and are typically employed to inspect a structure for defects. In general, high frequency sound waves are applied to the structure being tested using one or more transducers. The transducers typically comprise piezocrystal elements that are excited by an electrical voltage in order to induce the ultrasonic waves in the structure. When the sound waves interact with something (e.g., a void; a crack or other defect) having a significant difference in impedance from that of the propagation medium, a portion of the sound is either reflected or diffracted back to the source from which it originated. Detection and quantification of the returned sound pattern is used to determine the characteristics of the reflecting medium. The results obtained from the inspection are utilized to assess the condition and integrity of the structure. Assessment of the structure is based on the characteristics of the detected defects, such as, for example, the size, orientation and location of the defects. The more precise and accurate the inspection technique and data obtained therefrom, the more reliable is the assessment for determining the condition of the structure. It is desired to identify defects to preclude progression to a point where there is a risk to the integrity of the structure and potential structure failure. The consequences of a sudden failure of a structure in a system, such as, for example, an electrical power generation plant, could result in a severe situation.
Ultrasonic technology can provide for computer-controlled excitation (e.g., amplitude and delay) of a probe. The excitation of piezocomposite elements can generate a focused ultrasonic beam with the potential to modify beam parameters such as angle, focal distance, and focal point, through software. Thus, a computer-controlled beam scanning pattern can be implemented in order to “steer” (e.g., direct) the beam to the area of interest and to search for cracks or other discontinuities.
Piping designs and configurations can differ significantly in various systems, such as but not limited to the field of electrical power generation. Some piping systems consist of complex geometries having a plurality of curves, contours, and otherwise irregular geometries. Inspection of the piping using ultrasonic testing techniques is more difficult as the complexity of the geometry of the object to be tested increases. For instance, compound curves make ultrasonic testing very difficult because one portion of the compound curve may, for example, be convex and therefore function to diverge the ultrasonic wave being projected by the transducer while another portion may be, for example, concave and therefore, tend to converge the beam. As a result of the complexity of the design, commercially available ultrasonic inspection has been limited.
The nondestructive evaluation techniques known in the art typically use conventional guided waves which propagate for relatively long distances and therefore, allow for the inspection of a large volume from a single location. However, these conventional guided waves do not provide for the ability to detect smaller sized defects or defects in a difficult to reach area. Furthermore, the nondestructive evaluation techniques known in the art can be time consuming, difficult to implement and provide less than satisfactory results.
Thus, there is a need in the art to design and develop pipe inspection systems and methods that can be performed relatively quickly, are easily implemented and can provide accurate and detailed results which identify even small defects in piping systems having complex geometries. Further, there is a need to employ transducers other than the conventional guided waves used in known ultrasonic testing which can be limiting as to the size of defect which can be detected.